Process for digesting fibrous material



Patented July 29, 1930 SIDNEY D. WELLS, 0F QUINCY, ILLINOI IS PROCESS FOR DIGESTING FIBROUS MATERIAL No Drawing. Application filed July 11,

This invention relates to processes now in general use for removing from wood, straw, grass, bark and other fibrous plants, or portions thereof, the cellulose, ligno, pecto, onto or other forms or combinations of cellulose, for the purpose of using the same in the manufacture of paper pulp or other useful prod ucts, and comprises an improvement in the process disclosed in United States Patent N 0. 1,266,957 for Manufacture of wood pulp issued to myself and Otto Kress May 21, 1918. More specifically, the invention relates to improvements in the so-called soda and sulphate and similar processes for doing this work. In the customary processes for producing paper pulp from wood using alkalies or salts of the alkaline metals, the digesters are filled with Wood chips and a volume of solution of the alkali sufficient to introduce the required amount of the alkali and at the same time be sufficient in volume to provide proper distribution of the liquor by any of the means commonly employed such as centrifugal pumps, steam injectors, or rotation of the digester on trunnions. The cooking operation is then commenced with a considerable volume of air in the digester which is removed so far as possible by relieving or blowing oif steam from the digester while it is coming up to pressure or after it has attained the desired pressure. Furthermore, at the commencement of the cooking operation, the liquor has not reached the interior of the chips and it is only after the outer portions of the chips have been subjected to considerable digestion that the liquor comes in contact with the interior of the chips. It is well known that the influence of air on the cellulose content of the wood has a very deleterious effect on the quality and yield of pulp obtained. Furthermore, the delay in the penetration of the chips by the cooking liquor brings about the over-cooking of the outer portions of the chips and by the time the liquor has reached the inner portions, it has been very materially reduced in strength and activity so that the resulting pulp is composed of fibres cooked to widely diiferent degrees.

The invention consists in a complete re-organizatic-n of the foregoing old processes by 1925. Serial No. 42,978.

hereafter more fully described occur, the

Whole resulting in great economies in the amount of chemicals required, the amount of fuel required and in the time of operating-- these with increased yield of product and improved product.

fStated in other words, some of the objects 0 the digester before the cooking operation has started and thereby avoid the deleterious effect of the oxygen in the air in oxidizing the cellulose of the wood fibres which impair their strength and cause reduced yield of product; to save chemicals in cooking on account of the fact that the products of oxidation which neutralize the alkalinity of the liquors are avoided; to produce a more uniform product with less chemical, and with a in time on account of the greater uniformity of cooking and the smaller volumes of liquor that may be used when the chips are thorough- 1y impregnated; to render greater concentration of the cooking chemical possible, whereby there is greater activity and smaller amounts of steam are required to heat the smaller volumes employed.

The invention further consists in many features and details hereafter more fully set forth.

In the process of this invention,

ventional form of digester, well known in the art, is provided and charged with the desired quantity of raw material to be digested. The digester is then completely filled with the liquor which is .to act upon the material to digest it. The digester is then closed and more liquor is added under pressure until the digester reaches a. hydrostatic pressure of preferably in the neighborhood of 100.11: per square inch-although the operation will take place from, say, 20# up. The digester is left in this condition for-eat 100# pressure-about a half an hour, at'the end of which time it is found that the material the invention are: to remove the air from any conmaterial saving to be digested, of ordinary commercial size,

"withdrawn, preferably the digester to is thoroughly impregnated with the digesting l'i'q'uo'r =w ereupon the digester is opened, say atthebottom and'enough of the liquor is from the bottom and through'a strainer-,- to reduce the quantity in that ordinarily used in cooking, say from one-third to two-thirds of the capacity of the digester not occupied by the material to be digested. During the withdrawal of the excess liquor, referred to, steam is admitted insufficient quantity, preferably at," the top of the digester to keep the digester full and prevent the entrance of air. The digester is then heated and the process carried on in the ordinary conventional manner to'c'ook'.

'The'g'reat advantage of the invention is in -"replacing the liquor in the digester during impregnation'by steam admitted above the liquor level and thereby preventing air to enterthe digester. This must take place in a'll'known processes if the liquor is to be removed without creating a vacuum, and thus preventing attainment of the desired effect on" the product. The steps of this process can also 'be" combined with a preliminary s'teamingbefore-the liquor is introduced into the digester whereby a considerable amount ofairis removed and a vacuum is formed in each chip as the cool liquor is run in, the

result being that there is less air trapped in the chips to be removed later.

The alkalies or salts of alkaline metals referred toin the opening statement refer to compounds of the alkaline metals or earths such as the hydroxides, carbonates or bicarb'onates', sulphides, sulphites, thiosulphates and'similar sulphur compounds of the same and other compounds having an alkaline or reducing nature and exclude bisulphites or bther'compounds having an acid reaction which produce entirely diiferent effects and arefnot' included within the scope of this invention. j I

I-Iavirig'thus described my invention, what I'cla'im as new and desire to secure by Letters l atent' is: a I. the'a'rt described, the method of placing a predetermined quantity of material to be digested-in a-closed digester, complete- Ty filling-the digesterwith non-acid digestin lquon-" allowingthe filled digester to stani l tusuffieientflen thof time for the liquor to i-r'npregnatP -the";n1aterial to be digested, then removing a portion of the liquor from the Inver -portions of thedigester and simultameasly introducing. steam to occupy the space vacated by the liquor whereby to prevent-t tre flormationzlo'f a vacuum in the digester and thus to exclude air from the material being digested, all this preparatory to heating the digester and thereafter proceeding in conventional manner.

2. In the art described, the method of placing a predetermined quantity of material to be digested in a closed digester, completely filling the digester with non-acid digesting liquor to thereby exclude air from the digester, applying hydrostatic pressure to the contents of the digester, allowing the filled digester to stand a suflicient length of time for the liquor to impregnate the material to be digested, then withdrawing a quantity of the liquor from the lower portions of the digester and simultaneously introducing steam to occupy the space vacated by the liquor to thereby exclude air from the material being digested-this preparatory to heating the digester and proceeding in conventional manner.

3. In the art described, the method of placing a predetermined quantity of material to be digested in a closed digester, completely filling the digester with non-acid digesting liquor under hydrostatic pressure to thereby exclude air from the digester, thereafter allowing the filled digester to stand a sufficient length of time for the liquor to impregnate the material to be digested, then removing a quantity of the liquor from approximately the bottom of the digester and simultaneously introducing steam to occupy the space vacated by the liquor to thereby exclude air from the material being digested-this preparatory to heating the digester and proceeding in conventional manner.

4. The method of digesting fibrous material which consists in blanketing from the air a predetermined quantity of material to be digested by means of a nonacid liquor for a suflicient period of time to permit the liquor blanket to thoroughly impregnate the material to be digested, thereafter removing a portion of the liquor blanket and replacing same with steam in order to maintainexclusion of air fromthe material, thereafter proceeding in the conventional manner to cook the material.

5. In the process of digest'ng fibrous material, as a preliminary step of a predetermined quantity of material to be di ested in a closed container by completely filing the container with a suitable nonacid digesting liquor, permitting the filled digester to stand for a period of time sufficient to permit thorough impregnation of the material to be digested with the digesting liquor, thereafter removing a part of the digesting liquor from the digester while simultaneous introducing steam into the digester to occupy the space vacated by the removed liquor in .order to maintain the inclusion of air from the vdigester and finally heating the digester and proceeding in the conventional manner.

In witness whereof, I have scribed my name.

SIDNEY D. WELLS.

hereunto sub-- 

